Recently, in order to improve driving safety of a vehicle, there have been proposed systems that allow a driver to monitor an air pressure, temperature, etc. of a tire detected by a tire condition detection device mounted on a tire side (see patent documents 1, 2 and 3, for example), and the systems are coming into practical use.
In general, an antenna used for receiving a radio signal from the tire condition detection device is mounted on the inner surface of a fender where a tire is housed so as to be positioned as near as possible to the tire in order to gain good sensitivity. However, the strength of the radio wave allowed by Japanese legislation is very weak; it has found through actual vehicle running testing that the reception efficiency of the antenna receiving a radio signal from the tire condition detection device is greatly changed even if the attachment position of the antenna is slightly different.
At present, the above-mentioned antenna is mounted on the body side of a vehicle by threadedly securing the antenna contained in an antenna case to the inner surface of the fender having a plurality of tapped holes formed therein for attaching the antenna. To adjust the reception efficiency of the antenna, it is necessary to change the attachment position of the antenna; each time when the reception efficiency of the antenna is adjusted, it is required to form new tapped holes for attaching the antenna in the inner surface of the fender.
Normally, devices such as the antenna and the like are attached to the body of a vehicle, and the reception efficiency of the antenna is adjusted checking the conditions of the devices through actual vehicle running testing; when adjusted, new tapped holes for attaching the antenna are formed to change the attachment position of the antenna; this operation is troublesome, and a problem is that the adjustment of the reception efficiency of the antenna is not easy.
In particular in the case of vehicles such as trucks, dual wheels are used for their rear wheels, and when one antenna mounted on the body side of the vehicle receives a radio signal from each of tire condition detection devices placed within tires mounted on the dual wheels, the adjustment of the attachment position of the antenna is required.
Patent Document 1: Japanese Patent Application Kokai Publication No. 2002-225520
Patent Document 2: Japanese Patent Application Kokai Publication No. 2003-165465
Patent Document 3: Japanese Patent Application Kokai Publication No. 2003-165313